The overall objectives of this project are to increase our understanding of the interaction of ultrasound with tissue. Two complimentary approaches are taken: (a) From studies of the acoustic properties of tissues, physical processes and effects can be deduced, (b) From direct observations of biological effects we can postulate and test for the responsible mechanisms. Our specific goals for the coming year include: (1) Studies of the absorption of sound in macromolecular solutions, bacteria and tissues; (2) Extension of the studies on nonlinear phenomena in propagation of sound in tissues; (3) Tests of the cavitation hypothesis for effects of ultrasound on plant roots and Drosophila eggs; (4) Completion of the study of the effect of ultrasonic irradiation on rate of metastasis from malignant tissues.